In an afternoon update, American Airlines announced that it had canceled more than 1,200 flights, up from 775 earlier in the day. The airline, which had hoped to resume some service along the East Coast on Thursday afternoon, said it had canceled service to Boston; Providence, R.I.; Newark and New York’s LaGuardia for the remainder of the day. Officials said they hoped to resume service to those airports Friday.

American officials said they might start limited service at New York’s John F. Kennedy International on Thursday afternoon, if the current state of emergency is lifted by Gov. Andrew M. Cuomo (D). That announcement could come as early as 4 p.m.

The storm has forced the cancellation of more than 550 United Airlines flights, roughly 25 percent of the airline’s schedule. United operates a large international hub at Newark’s Liberty International, where more than three-quarters of scheduled departures were grounded Thursday.

Flights bound for New York’s JFK are being diverted to airports as far away as Chicago and Atlanta. Airports in the D.C. region, which has been less affected by the winter storm, are accommodating flights unable to land at international gateways in New York and Philadelphia.

Nearly a dozen international flights from JFK and Philadelphia have instead landed at Dulles International. In some cases, passengers will remain on the planes while they refuel but in others, passengers have been taken off the planes, gone through customs and will travel to New York by buses provided by the airlines, said airport spokesman Andrew Trull.

Several flights have also been diverted to Baltimore-Washington International Marshall.

Earlier post:

Airlines canceled more than 3,000 flights Thursday as a massive winter storm known as a “bomb cyclone” blanketed cities up and down the East Coast in snow.

Airports remained open, but hundreds of flights to Boston, New York, New Jersey and Philadelphia were grounded. By early Thursday, American Airlines said it had canceled more than 775 flights. The airline’s travel advisory now covers 35 airports, including New York’s LaGuardia.

Airport operations are normal this morning, but #WinterStormGrayson is impacting air travel to other parts of the east coast. Check with your air carrier for flight delays, cancellations and flexible rebooking options.

The airline said it canceled shuttle service to LaGuardia and Boston’s Logan International airports. Officials said operations may resume later in the day depending on weather. (See below for more details about American’s operations.) Wednesday afternoon, Delta Air Lines announced it had canceled more than 400 flights.

Airlines often will cancel flights ahead of weather disturbances and reposition aircraft to allow them to restart operations as soon as conditions improve. In the case of Thursday’s storm, moving aircraft out of airports in New York and Boston also frees up space to allow airport officials to clear snow from runways and taxiways.

In most cases, airlines said they will waive fees for passengers with tickets on affected flights.

A massive winter storm known as a "bomb cyclone" crawled up the East Coast on Jan. 4 with blizzard conditions. (WUSA9)

D.C. area airports remained open but advised travelers to check with their airlines before heading out. Airport officials also urged those whose flights are operating to allow extra time to get to the airport because of icy conditions on area roadways.

Conditions at BWI is Snow with reduced visibility so please allow extra time on the roads. Flights are being impacted by weather so please check with your airline to see if your flight is being impacted.

American Airlines officials said all flights in and out of LaGuardia have been canceled until 3 p.m. Eastern. The airline said it planned to allow limited arrivals at Bradley International Airport in Hartford, Conn., and T.F. Green International Airport in Providence, R.I., around 8 p.m.

In Boston, the airline said it may allow limited arrivals at 7:30 p.m.

A "bomb cyclone" is moving along the East Coast and it's expected to bring more bitter cold and dump some snow. This is how the weather event originates. (Claritza Jimenez/The Washington Post)